<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
  .outer {
      height: 100px;
      background-color: yellowgreen;
      display: flex;
      justify-content: center;
      align-items: center;
  }
</style>
<body>
<div class="outer">
    <div>1</div>
</div>
</body>
</html>
